summaryrefslogtreecommitdiff
path: root/extensions/libxt_length.c
blob: 96e8b6cd8e7daf90e8dc8c30a03bf525ca3c8cfd (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
/* Shared library add-on to iptables to add packet length matching support. */
#include <stdio.h>
#include <netdb.h>
#include <string.h>
#include <stdlib.h>
#include <getopt.h>

#include <xtables.h>
#include <linux/netfilter/xt_length.h>

static void length_help(void)
{
	printf(
"length match options:\n"
"[!] --length length[:length]    Match packet length against value or range\n"
"                                of values (inclusive)\n");
}
  
static const struct option length_opts[] = {
	{ "length", 1, NULL, '1' },
	{ .name = NULL }
};

static u_int16_t
parse_length(const char *s)
{
	unsigned int len;
	
	if (!xtables_strtoui(s, NULL, &len, 0, UINT32_MAX))
		xtables_error(PARAMETER_PROBLEM, "length invalid: \"%s\"\n", s);
	else
		return len;
}

/* If a single value is provided, min and max are both set to the value */
static void
parse_lengths(const char *s, struct xt_length_info *info)
{
	char *buffer;
	char *cp;

	buffer = strdup(s);
	if ((cp = strchr(buffer, ':')) == NULL)
		info->min = info->max = parse_length(buffer);
	else {
		*cp = '\0';
		cp++;

		info->min = buffer[0] ? parse_length(buffer) : 0;
		info->max = cp[0] ? parse_length(cp) : 0xFFFF;
	}
	free(buffer);
	
	if (info->min > info->max)
		xtables_error(PARAMETER_PROBLEM,
		           "length min. range value `%u' greater than max. "
		           "range value `%u'", info->min, info->max);
	
}

static int
length_parse(int c, char **argv, int invert, unsigned int *flags,
             const void *entry, struct xt_entry_match **match)
{
	struct xt_length_info *info = (struct xt_length_info *)(*match)->data;

	switch (c) {
		case '1':
			if (*flags)
				xtables_error(PARAMETER_PROBLEM,
				           "length: `--length' may only be "
				           "specified once");
			xtables_check_inverse(optarg, &invert, &optind, 0, argv);
			parse_lengths(optarg, info);
			if (invert)
				info->invert = 1;
			*flags = 1;
			break;
			
		default:
			return 0;
	}
	return 1;
}

static void length_check(unsigned int flags)
{
	if (!flags)
		xtables_error(PARAMETER_PROBLEM,
			   "length: You must specify `--length'");
}

static void
length_print(const void *ip, const struct xt_entry_match *match, int numeric)
{
	const struct xt_length_info *info = (void *)match->data;

	printf("length %s", info->invert ? "!" : "");
	if (info->min == info->max)
		printf("%u ", info->min);
	else
		printf("%u:%u ", info->min, info->max);
}

static void length_save(const void *ip, const struct xt_entry_match *match)
{
	const struct xt_length_info *info = (void *)match->data;

	printf("%s--length ", info->invert ? "! " : "");
	if (info->min == info->max)
		printf("%u ", info->min);
	else
		printf("%u:%u ", info->min, info->max);
}

static struct xtables_match length_match = {
	.family		= NFPROTO_UNSPEC,
	.name		= "length",
	.version	= XTABLES_VERSION,
	.size		= XT_ALIGN(sizeof(struct xt_length_info)),
	.userspacesize	= XT_ALIGN(sizeof(struct xt_length_info)),
	.help		= length_help,
	.parse		= length_parse,
	.final_check	= length_check,
	.print		= length_print,
	.save		= length_save,
	.extra_opts	= length_opts,
};

void _init(void)
{
	xtables_register_match(&length_match);
}